Developing apparatus comprising excessive toner separation means

ABSTRACT

A developing apparatus uses a dual-component developer containing a magnetic carrier and toner electrically attracted to the magnetic carrier for selectively transferring the toner to an electrostatic latent image formed on an image support for visualizing the latent image. The developing apparatus includes a developer transport member facing the image support and having a peripheral surface for supporting and transporting the developer. A toner excess supplying member supplies excess toner to the developer supported on the developer transport member. An excess toner separator separates toner having a small adhesion force to the carrier from the developer to which excessive toner is applied.

BACKGROUND OF THE INVENTION

This invention relates to a developing apparatus which uses adual-component developer containing a magnetic carrier and tonerelectrically attracted to the magnetic carrier and selectively transferstoner in the dual-component developer to a latent image formed on animage support for visualizing the latent image.

In electrophotographic techniques, a developing method using adual-component developer containing toner and a magnetic carrier has theadvantages that toner is easily charged and that flocculation of tonerparticles is hard to occur. Thus, hitherto, the method has been widelyused although it requires control of the toner amount contained in thedual-component developer, namely, the toner density.

FIG. 15 is a schematic diagram to show the configuration of an exampleof a conventionally known developing apparatus using a dual-componentdeveloper.

The developing apparatus comprises a developing roll 202 placed near andfacing an image support 201 for magnetically attracting a developer andtransporting it, a developer regulation member 203 for regulating thedeveloper amount attracted on the developing roll 202 as an almostuniform magnetic brush, a paddle 204 for supplying the developer to thedeveloping roll 202, and two augers 205 and 206 for transporting andagitating the developer in a housing 210.

The developing roll 202 comprises a magnet roll 211 fixedly supportedand a cylindrical sleeve 212 rotated in the surroundings of the magneticroll for attracting a developer on the sleeve by the magnetic roll 211and transporting the developer to a section opposed to the image support201 by rotating the sleeve 212.

The two augers 205 and 206 rotate so as to transport a developer inopposite directions in two agitation chambers disposed behind thedeveloping roll 202 for circulating the developer in the two agitationchambers communicating with each other at both ends.

In the developing apparatus, the carrier and toner contained in adeveloper are sufficiently agitated in the agitation chambers 207 and208 and a part of the developer is supplied to the developing roll 202.The developer is attracted on the sleeve 212 by a pick-up magnetic pole213 of the magnet roll 211 and its layer thickness is regulated by thedeveloper regulation member 203, then the developer is transported to adeveloping area for development.

The developer passing through the developing area is released from thesleeve 212 by a pick-off magnetic pole 214 and is restored to theagitation chamber by the paddle 204. In the agitation chamber, therestored developer is mixed with the remaining developer and new tonerreplenished and is sufficiently agitated.

The charge amount of toner in a developer used with the developingapparatus varies depending on the environmental conditions and alsovaries greatly depending on the toner concentration in the developer.FIG. 16 shows the relationship between the toner density and tonercharge amount in the developing apparatus using a dual-componentdeveloper as described above under environmental conditions of hightemperature, high humidity, medium temperature, medium humidity, lowtemperature and low humidity. Generally, the toner charge amount changesaccording to characteristics as shown in FIG. 16; the toner chargeamount must be maintained constant to provide a constant developingcharacteristic under each environmental condition. To hold the tonercharge amount constant, the following control needs to be performed:

When the operating environment changes from high temperature andhumidity (state indicated by character w in FIG. 16) to mediumtemperature and humidity (state indicated by character x' in FIG. 16),toner must be replenished for raising the toner density from W to X toset a state in which the toner charge amount becomes a predeterminedvalue (state indicated by character x' in the figure). When theenvironmental condition changes from low temperature and humidity (stateindicated by character y in FIG. 16) to medium temperature and humidity(state indicated by character z in FIG. 16), the toner density must belowered from Y to X for setting a state in which the toner charge amountbecomes a predetermined value (state indicated by character x in thefigure). However, the conventional developing apparatus using adual-component developer simply consumes toner as means for lowering thetoner density, in which case, the toner charge amount lessens and theimage density lowers

To control the toner density, a reference image is actually developedand its density is sensed for replenishing toner in response to thesensed density; a complicated control method and apparatus are required.From these circumstances, a developing apparatus with a simple mechanismfor controlling the toner density for providing a stable-density imageis described in the Unexamined Japanese Patent Application PublicationNo. Sho. 52-15334, the Examined Japanese Patent Application PublicationNo. Hei. 5-59427, and the Unexamined Japanese Patent ApplicationPublication No. Hei. 7-84456, for example.

In the technique described in the Unexamined Japanese Patent ApplicationPublication No. Sho. 52-15334, a used developer is recovered in astorage tank, which is replenished with a sufficient amount of toner,then the mixture is agitated and charged. Excessive toner particles areremoved and the developer is taken out with toner particles adhering tocarrier in a saturation state, and is again transported to thedeveloping apparatus for development.

In the technique described in the Examined Japanese Patent ApplicationPublication No. Hei. 5-59427, the point of a magnetic brush on a sleeveis scrubbed with toner in a toner hopper through a mesh screen, wherebythe adhesion amount of toner to a magnetic carrier is made stable.

In the technique described in the Unexamined Japanese Patent ApplicationPublication No. Hei. 7-84456, a developing roller is surrounded by anarrow space and the carrier amount in the space is made almostconstant, whereby the amount of toner stored in the remaining space isadjusted for controlling the toner density to an almost constant value.

However, the developing apparatuses as described above involve thefollowing problems:

The developing apparatus described in the Unexamined Japanese PatentApplication Publication No. Sho. 52-15334, which agitates a developermechanically, has the disadvantage that a large stress is imposed on thedeveloper, causing toner fusion to the carrier and adhesion of anexternal additive to toner. Further, the developer is once moved to thestorage tank where it is agitated, thus upsizing the apparatus isinevitable and manufacturing costs also increase.

The developing apparatus described in the Examined Japanese PatentApplication Publication No. Hei. 5-59427 scrubs a developer through themesh screen, thus a stress is imposed on the developer, resulting indrastic lowering of the lifespan of the developer. Since the flowproperty of toner or the charge property of toner, namely, adhesionforce of toner and carrier contribute largely to control of the tonerdensity, if the flow property or charge property of toner changesdepending on the environment or over time, the toner density controlrange is placed out of the initially setup range and the print imagequality becomes different from the initial one.

Application where solid images having gradation, such as photos,pictures, or maps, are mainly printed and application where line imagesare mainly printed differ largely in replenished toner amount; since thecontract area between carrier and toner is limited in the mesh screenmethod, when the replenished toner amount largely changes, it becomesdifficult to maintain the toner density constant.

Further, the developer is replenished with toner with the magnetic brushformed on the magnet roll; normally the developer is in a flocculationstate, thus the effective charge area of carrier decreases andcharge-failure toner becomes prone to occur.

The technique described in the Unexamined Japanese Patent ApplicationPublication No. Hei. 7-84456, which uses magnetic toner, requires thatmagnetic power be contained in toner; magnetic power cannot be mixedwith color toner from the coloring property problem and color tonercannot be used. If an attempt is made to non-magnetize toner withimportance attached to the coloring property, the disclosed techniquedoes not provide the developing apparatus function. That is, ifnonmagnetic toner is used with the developing apparatus, nonmagnetictoner and magnetic carrier are not agitated and are stored in a narrowspace, thus toner is charged insufficiently. The toner, which is free ofa scatter prevention effect of a magnetic force, easily becomes a cloud;a large amount of toner cloud appears on an image as fog and prints of agood image quality cannot be provided.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a developingapparatus that can control the toner density and toner charge amount ina dual-component developer by a simply structure and provide a goodimage quality stably even if the toner use amount changes when theenvironmental conditions change or due to the original documentdifference.

To the end, according to the invention, there is provided a developingapparatus using a dual-component developer containing a magnetic carrierand toner electrically attracted to the magnetic carrier for selectivelytransferring the toner to an electrostatic latent image formed on animage support for visualizing the latent image, wherein an excess oftoner is supplied to the developer passing through a developing area andthen recovered from a developer transport member, then toner having asmall adhesion force to the carrier is separated from the developer byexcessive toner separation means. The developer from which the excessivetoner is separated is again supplied to the developing area.

In the developing apparatus, when toner is supplied excessively and isagitated, it is charged. Then, excessive toner having a small adhesionforce to the carrier is separated from the developer by the excessivetoner separation means.

The carrier charge amount at this time becomes almost constantindependently of environmental conditions and the average charge amountof toner particles adhering to the carrier and the toner amount alsobecome constant. That is, the toner density and the toner charge amountof the developer from which the excessive toner is separated becomealmost constant. The developer is supported on the developer transportmember and transported for development, whereby a stable-density imagecan be formed even if the environmental conditions change.

The excessive state of toner is a state in which the developer containstoner exceeding a toner density enough to execute proper developing inthe developing area.

The cause indicating environmental resistance as described above isguessed as follows: Noting the carrier and toner charge properties, thetoner charge property can show stronger environmental dependency thanthe carrier charge property, because the probability that a chain with acut polymer exists on the toner surface because of the tonermanufacturing method is high, and the cut chain, which is active, easilyreacts with water and is prone to undergo environmental change. On theother hand, the carrier usually is coated with a coating material andthus is hard to undergo environmental change unlike the toner.Therefore, in the conventional system, the developer contains a smallamount of toner and the charge amount of the developer is in anunsaturation state for the carrier charge capability, thus the tonercharge property becomes predominant and environmental dependency isshown. However, in the system of the invention, an excess of toner issupplied to a developer, then excessive toner is separated from thedeveloper. Since the charge amount of the developer becomes a saturationstate for the carrier charge capability, the carrier charge propertybecomes predominant and environmental dependency is not shown.

In the developing apparatus according to the invention, the area inwhich an excess of toner is supplied to the developer and agitated isset to a position where a magnetic force little acts and magneticcarriers do not form a sequence, whereby the desirable result isprovided. That is, toner is supplied and agitated in the area in which amagnetic force little acts as described above, whereby carrier particlesdisperse and all the surface area comes in contact with the toner,promoting charging the toner. The toner is electrically attracted on allthe surface area. Therefore, a developer with toner attracted on thecarrier in an electric saturation amount can be supplied stably fordevelopment.

On the other hand, a toner excess supplying member is disposed at aposition along the outer peripheral surface of a sleeve and a pluralityof magnetic poles are disposed in a portion of a magnetic fieldgeneration member opposed to the toner excess supplying member as analternating pattern of N and S poles, whereby excessively supplied tonercan also be sufficiently agitated and charged. The developer having thetop to which an excess of toner is supplied in the toner excesssupplying member forms a magnetic brush as an ear on the sleeve by amagnetic force of the magnetic field generation section and istransported by rotation of the sleeve. At this time, since the magneticpoles in the portion of the magnetic field generation member opposed tothe toner excess supplying member form an alternating pattern of N and Spoles in the circumferential direction, the magnetic brush tumbles inthe direction of the magnetic force line on the sleeve and rotation ofthe magnetic brush by which the upper developer portion moves to thelower part and the lower developer portion moves to the upper part, orso-called tumbling occurs. Thus, excessively supplied toner is takeninto the developer inside and sufficiently agitated.

In the developing apparatus, for example, a sieve member provided with alarge number of openings each sized for blocking the magnetic carrierand allowing toner to pass therethrough can be used as the excessivetoner separation means. If such a sieve member is used, the developer towhich an excess of toner is supplied and which is agitated passesthrough the top of the sieve member, toner having a small adhesion forceto the carrier passes through the openings of the sieve member andexcessive toner in the developer is separated. At this time, withfurthermore charging, the developer has toner adhering to carrier in aamount for entering a saturation state corresponding to carrier charges.

The sieve member may be shaken mechanically or electrically or thedeveloper on the sieve member may be shaked, whereby separation ofexcessive toner is promoted and a developer stable in toner density canbe provided reliably.

As another example, the excessive toner separation means may havemagnetic field generation means with an alternating pattern of N and Spoles magnetized along the outer peripheral surface, and a sleeve havinga peripheral surface supported for circumferential rotation outside themagnetic field generation means for magnetically attracting thedeveloper on the peripheral surface and transporting the developer. Inthe excessive toner separation means, a magnetic brush of a developerwith an ear of magnetic carriers is transported while tumbling isgenerated by a circumferential rotation move of the sleeve or rotationof the magnetic field generation means. Toner having a small adhesionforce to the carrier is separated by agitation of the tumbling.

As still another example, the excessive toner separation means may havemagnetic field generation means for generating a changing magnetic fieldin the housing of the developing apparatus for agitating and pulling upa developer by a magnetic force and supplying the developer to thedeveloper transport member. For example, the magnetic field generationmeans may be a magnet supported for rotation behind the wall face of thehousing for storing the developer. That is, as the magnet rotates,magnetic poles move, generating a changing magnetic field, whereby thedeveloper in the developing apparatus can be pulled up and toner havinga small adhesion force to the carrier is separated from the developer,whereby a developer almost stable in the toner density and toner chargeamount can be supplied to the developer transport member; even if theenvironmental conditions change, a stable-density image can be provided.

Preferably, the magnet supported for rotation is a roll member with analternating pattern of S and N poles magnetized on the peripheralsurface.

As another example, the magnetic field generation means may be aplurality of electromagnets arranged along the wall face of the housing.That is, the current direction and timing are controlled for energizingthe electromagnets, whereby a changing magnetic filed can be generatedfor pulling up the developer in the developing apparatus. Excessivetoner can be separated from the developer and supplied to the developertransport member.

The developing apparatus may further include a toner resupply member fortransporting the toner separated by the excessive toner separation meansto the toner excess supplying member, whereby the separated toner can berecycled smoothly.

The invention is not limited to a dual-component magnetic brushdeveloping apparatus and can also be applied to a so-called hybriddeveloping apparatus using a dual-component developer and causing adeveloping area only to function as mono component developing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram to show the configuration of a developingapparatus of one embodiment of the invention;

FIG. 2 is an illustration to show the toner density and the toner chargeamount in steps of the developing apparatus;

FIG. 3 is an illustration to show an experiment for checking the chargeeffect of toner when excessive toner is separated from a developercontaining an excess of toner;

FIG. 4 is a schematic diagram to show the configuration of a developingapparatus of another embodiment of the invention;

FIG. 5 is a schematic diagram to show the configuration of a developingapparatus of one embodiment of the invention;

FIG. 6 is a schematic diagram to show the configuration of a developingapparatus of one embodiment of the invention ;

FIG. 7 is a schematic diagram to show the configuration of a developingapparatus of one embodiment of the invention;

FIG. 8 is a schematic diagram to show the configuration of a developingapparatus of one embodiment of the invention;

FIG. 9 is a schematic diagram to show the configuration of a developingapparatus of one embodiment of the invention;

FIGS. 10A to 10C are perspective views to show magnetic polearrangements of magnet rolls used with the developing apparatus shown inFIG. 9;

FIG. 11 is a schematic diagram to show the configuration of a developingapparatus of another embodiment of the invention;

FIG. 12 is a schematic diagram to show the configuration of a developingapparatus of one embodiment of the invention;

FIG. 13 is a schematic diagram to show the configuration of a developingapparatus of one embodiment of the invention;

FIG. 14 is a perspective view to show a spiral auger used with thedeveloping apparatus shown in FIG. 13;

FIG. 15 is a schematic diagram to show the configuration of aconventional developing apparatus; and

FIG. 16 is a graph to show the relationship between the toner densityand toner charge amount in the conventional developing apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, there are shown preferredembodiments of the invention.

FIG. 1 is a schematic diagram to show the configuration of a developingapparatus of one embodiment of the invention.

The development apparatus has a developing roll 2 being placed in ahousing 10 for storing a dual-component developer for supporting thedual-component developer on the peripheral surface of the developingroll 2 and transporting the developer to an area opposed to an imagesupport 1, a developer regulation member 3 for regulating the amount ofthe dual-component developer supported on the developing roll 2, a guideplate 4 for recovering the developer passing through a developing areaand then stripped off from the developing roll 2 to a toner excesssupplying member A, a paddle 5 for supplying toner to the toner excesssupplying member A, and a mesh member (sieve member) for siftingexcessive toner from the developer in the lower part of the toner excesssupplying member A. Further, a toner box (not shown) for replenishingthe housing 10 with toner is linked to the axial end of a toner storagesection 10a provided with the paddle 5.

The developing roll 2 comprises a magnetic field generation member 11having a plurality of magnetic poles in the circumferential directionand a hollow cylindrical sleeve 12 supported on the outside of themagnetic field generation member 11 for circumferential rotation. Themagnetic field generation member 11 forms a magnetic brush of adual-component developer on the surface of the sleeve 12 by a magneticfield formed between the adjacent magnetic poles. As the sleeve 12rotates, the magnetic brush can be transported to the developing area.

Magnetic poles 11a and 11b of the same polarity in the magnetic fieldgeneration member 11 are disposed at adjacent positions and a developerstripped off from the developing roll 2 by a repulsion magnetic filed ofthe two magnetic poles slips down along the guide plate 4 bygravitation. The surface of the guide plate 4 is coated with fluororesinto make the developer smoothly slip down or a carrier coat agent toaccelerate start-up when toner is charged. The developer slipping downalong the guide plate 4 is transported to an area not affected by themagnetic force of the magnetic field generation member 11; the areaforms the toner excess supplying member A. A partition plate 14 isattached to the guide plate 4 in the proximity of the developing roll 2for preventing a toner cloud occurring due to toner replenishment orseparation from being deposited on the developing roll 2.

The mesh member 6 has a large number of openings of the size forblocking a carrier and allowing toner to pass therethrough; in theembodiment, each opening is set to the size of about 30 μm because thecarrier diameter is 50 μm and the toner diameter is 7 μm. The meshmember 6 is disposed so as to incline in the direction of the developingroll 2 for receiving the developer slipping down along the guide plate 4and allowing the developer to slip down on the mesh member 6 bygravitation.

The paddle 5, which is disposed in the toner storage section 10a in thehousing 10, rotates in the arrow direction shown in FIG. 1, therebysufficiently agitating toner and supplying an excess of toner to thetoner excess supplying member A. A film member 7 coming in contact withthe mesh member 6 at the rotation time is bonded to the tip of thepaddle 5 for shaking the mesh member 6 as the paddle 5 rotates. The filmmember 7 uses a PET film 50 μm thick, but material, etc., of the filmmember 7 is not limited if the member shakes the mesh member 6.

The toner storage section 10a communicates with the lower part of themesh member 6 and toner passing through the mesh member 6 is restored tothe toner storage section 10a.

The dual-component developer used with the developing apparatus of theembodiment is a mixture of nonmagnetic polyester family toner and aferrite family magnetic carrier, but toner or a carrier made of anyother material can also be used.

In the developing apparatus, the developer, after it is supported on thedeveloping roll 2 and passes through the developing area, is strippedoff from the developing roll 2 by the action of the magnetic poles 11aand 11b of the same polarity. The stripped-off developer slips downalong the guide plate 4 by gravitation and is guided to the toner excesssupplying member A. As the paddle 5 rotates, an excess of new toner issupplied to the developer for temporarily raising the toner density inthe developer. The value of this toner density, which slightly changesdepending on the specific gravity of the carrier and toner used, liesmostly in the range of 20 wt % to 30 wt %. That is, since the normaltoner density is 2% to 10% or so when a ferrite family carrier iscontained in the developer, or is 6% to 20% when an MT family carrier iscontained, the toner density when an excess of toner is suppliedcorresponds to twice to 15 the general toner density.

The developer is moved to the mesh member 6 by gravitation. It slipsdown along the slope of the mesh member 6 by gravitation. As the meshmember 6 comes in contact with the film member 7 and is shaken,excessive toner in the developer is screened through the openings intothe toner storage section 10a. At this time, in the developer, onlytoner coming in contact with the carrier and charged is held andredundant toner not charged is screened out through the openings,whereby redundant toner having a small charge amount is removed from thedeveloper whose toner density is raised in the toner excess supplyingmember A, resulting in the toner density corresponding to the carriercharge capability.

Then, the developer is transported to the position opposed to thedeveloping roll 2 and a magnetic brush of the dual-component developeris formed on the developing roll 2. The developer is transported bycircumferential rotation of the sleeve 12 and the height of the point ofthe magnetic brush is regulated by the developer regulation member 3,then the developer is transported to the developing area. Toner in themagnetic brush is transferred to a latent image on the image support 1by an electric field formed in the developing area. The magnetic brushpassing through the developing area is then stripped off from thedeveloping roll 2 and again undergoes the above-mentioned process.

On the other hand, the toner passing through the mesh member 6 in theprocess is raked out by the paddle 5 and is restored to the tonerstorage section 10a. As the paddle 5 rotates, the toner is sufficientlyagitated and is again supplied to the developer in the toner excesssupplying member A as supply toner.

Although the developing apparatus has the toner box linked to the tonerstorage section 10a for replenishing the toner storage section 10a withtoner, the toner storage section 10a itself may be a replaceable tonercartridge.

A roller and a brush member may be disposed in place of the guide plate4 and the partition plate 14, whereby the developer can be easilystripped off from the developing roll. Further, as the members rotate,the developer and the mesh member can also be shaken reliably.

FIG. 2 is an illustration to show change of the toner density and thetoner charge amount as the above-mentioned process is executed.

According to the illustration, it is seen that the charge amount and thetoner density become almost constant values by executing the process asdescribed above no matter how much the toner charge amount is regardlessof the developing or non-developing portion before the toner density isset to a comparatively high density. It is guessed that the process ofseparating redundant toner from the state in which the toner density ishigh results in a state in which the carrier can hold toner reasonably,namely, the toner density fitted to the charge capability of the carriercoming in contact with toner and charged. That is, since the carrier isreleased from the point of the magnetic brush in an area not affected bythe magnetic force of the magnetic field generation member 11, thecarrier can move comparatively freely and the surface area of thecarrier increases; the number of times the carrier comes in contact withtoner increases. Thus, the state in which the toner density is high canbe easily created and redundant toner is also screened out smoothly; thestate in which the carrier can hold toner reasonably can be created.

Next, to examine the charge effect of toner when passing through themesh member, the charge state was checked using an apparatus as shown inFIG. 3. In the apparatus, a developer 20 high in toner density is storedin a tray 15 and a bar magnet 17 is made to approach the developer viaan opening member 16 having a large number of openings through which amagnetic carrier can pass narrowly for pulling up the developer.Resultantly, when the developer passes through the opening member 16,the toner is charged and the pulled-up developer contain almost constantcharge amount and toner density. Thus, the developing apparatus canproduce a good charge effect even with a small amount of developer andapparatus downsizing is enabled.

FIG. 4 is a schematic diagram to show the configuration of a developingapparatus of another embodiment of the invention.

The developing apparatus further includes a shaking member 28 supportedso as to come in contact with a mesh member 26 in addition to thedeveloping apparatus shown in FIG. 1. The shaking member 28 mechanicallyshakes the mesh member 26 by a motor; it can shake the mesh member 26little by little. The developing apparatus is the same as that shown inFIG. 1 in other components.

The developing apparatus can smoothly screen out toner having a smalladhesion force to a carrier from a developer by shaking the mesh member26. Thus, the sieve effect when excessive toner is separated improves.

FIG. 5 is a schematic diagram to show the configuration of a developingapparatus of one embodiment of the invention.

The developing apparatus has a plate-like electrode member 38 opposed toand above a mesh member 36 and an AC power supply 39 is connected to theelectrode member 38. The mesh member 36 is formed of a conductivematerial and is electrically grounded. The developing apparatus is thesame as that shown in FIG. 1 in other components.

In the developing apparatus, an AC voltage applied from the AC powersupply 39 causes an electric field to be formed between the electrodemember 38 and the mesh member 36, and the mesh member 36 is shaken inresponse to change in the electric field, whereby toner having a smalladhesion force to a carrier is screened out from a developer on the meshmember 36 and the separation effect of excessive toner improves.

FIG. 6 is a schematic diagram to show the configuration of a developingapparatus of one embodiment of the invention.

The developing apparatus comprises a frame 48 opposed to and above amesh member 46 and a shaking member 49 is attached so as to come incontact with the frame 48. The developing apparatus is the same as thatshown in FIG. 1 in other components.

In the developing apparatus, the frame 48 is mechanically shaken by theshaking member 49, shaking a developer above the mesh member 46, wherebyredundant toner having a small adhesion force to a carrier in thedeveloper is screened out and passes through the mesh, member 46 forseparation. Thus, the separation effect of excessive toner furthermoreimproves.

FIG. 7 is a schematic diagram to show the configuration of a developingapparatus of one embodiment of the invention.

The developing apparatus comprises a housing 60 containing a developingroll 52 having a magnetic field generation member 61 (magnet roll)having magnetic poles 61a and 61b magnetized to the same polarityrelative to the circumferential direction, magnetic poles 61c, 61d, and61e for transporting a developer to a developing area, and a developeragitation magnetic pole group 61f consisting of an alternating patternof N and S poles in the circumferential direction in a smaller spacingthan other magnetic poles. The neighborhood of the sleeve outerperipheral surface outside the position of the developer agitationmagnetic pole group 61f provides a toner excess supplying member. Tonerdipped up by a paddle 55 from a toner storage section 60a passes througha transport passage 60b and is supplied to the toner excess supplyingmember.

The developing apparatus is the same as that shown in FIG. 1 in othercomponents of developer regulation member 53, guide plate 54, paddle 55,mesh member 56, sleeve 62 of the developing roll, etc.

In the developing apparatus, an excess of toner in the toner excesssupplying member is supplied to the top of a magnetic brush of adeveloper with an ear of magnetic carriers and as the sleeve 62 rotates,the magnetic brush is transported in the circumferential direction. Atthis time, the magnetic brush tumbles in the direction of the magneticforce line of the developer agitation magnetic pole group 61f formed onthe sleeve 62, and rotation of the magnetic brush by which the upperdeveloper portion moves to the lower part and the lower developerportion moves to the upper part, or so-called tumbling occurs, wherebyexcessive toner supplied to the upper portion of the developer issufficiently taken into the developer inside and agitated for making auniform toner distribution, and friction of toner and carrier causescharging.

Then, the developer is stripped off from the developing roll 52 by arepulsion magnetic field of the magnetic poles of the same polarity, 61aand 61b, disposed in the magnetic field generation member 61, and ismoved along the guide plate 54 to the mesh member 56. Since the magneticforce of the magnetic generation member 61 little acts on the guideplate 54 and the mesh member 56, magnetic carriers can movecomparatively freely and almost all area of the magnetic carrier surfacecomes in contact with toner; charged toner can be attracted on almostall the magnetic carrier face. Further, when the developer slips downalong the slope of the mesh member 56 by gravitation, redundant tonerhaving a small charge amount in the developer is shaken off, resultingin the toner density matching the carrier charge capability. Thedeveloper is again supplied to the developing roll 52 and is transportedto the developing area by circumferential rotation of the sleeve 62 fordeveloping a latent image.

The developing apparatus, which agitates the developer to whichexcessive toner is supplied by tumbling as described above, can supplytoner into the developer more uniformly.

FIG. 8 is a schematic diagram to show the configuration of a developingapparatus of one embodiment of the invention.

The developing apparatus uses excessive toner separation meanscomprising an excessive toner separation magnet roll 83 rotated axiallyin a housing 80 and an excessive toner separation sleeve 84 fixedlysupported outside the magnet roll 83.

The excessive toner separation magnet roll 83 is a cylindrical magnetconsisting of an alternating pattern of S and N poles magnetized in thecircumferential direction and is rotated in the direction of arrow D1shown in FIG. 8. The excessive toner separation sleeve 84 is a fixedlysupported cylindrical member made of a nonmagnetic material. A developeris transported in the direction of arrow D2 along the outer peripheralsurface of the excessive toner separation sleeve 84 by rotation of amagnetic brush as an ear produced by change in a magnetic fieldgenerated by rotation of the excessive toner separation magnet roll 83,or so-called tumbling.

The components of the developing apparatus, such as a developing roll72, a developer regulation member 73, and a guide plate 74, areidentical with those of the developing apparatus shown in FIG. 1.

A paddle 75 disposed in a toner storage section 80a has the samestructure as the paddle of the developing apparatus shown in FIG. 1; itis rotated in an opposite direction for dipping up toner and supplyingthe toner through an opening 80b made in the upper part of the tonerstorage section 80a.

In the developing apparatus, a developer passing through a developingarea has toner consumed, is stripped off from the developing roll 72 bya repulsion magnetic field formed by magnetic poles magnetized to thesame polarity, 81a and 81b, and slips down along the guide plate 74. Anexcess of toner is supplied to the developer from the toner storagesection 80a.

The developer with excessive toner is magnetically attracted on theexcessive toner separation sleeve 84 and is transported along the outerperipheral surface of the excessive toner separation sleeve 84 by changein a magnetic field generated by rotation of the excessive tonerseparation magnet roll 83. At this time, the developer on the excessivetoner separation sleeve 84 is agitated by tumbling a magnetic brush ofdeveloper as an ear and excessive toner having a small adhesion force toa carrier in the developer is screened out.

Thus, the excessive toner in the developer is separated and thedeveloper set to the toner density matching the carrier chargecapability is supplied to the developing roll 72. Resultantly, thecharge amount of toner transported to the developing area becomes almostconstant, providing an image stable in density.

In the embodiment, the excessive toner separation magnet roll 83 isrotated and the excessive toner separation sleeve 84 is fixed, but theformer may be fixed and the latter may be rotated. Alternatively, theymay be rotated in the same direction or opposite directions with a speeddifference therebetween.

FIG. 9 is a schematic diagram to show the configuration of a developingapparatus of one embodiment of the invention.

The developing apparatus has a magnetic roll 96 supported for rotationbehind a wall face 100b of a housing for storing a developer asexcessive toner separation means. On the other hand, the housing 100 isformed with a developer agitation storage section B separated from atoner storage section 100a by a partition 98, and a guide member 94 fortransporting a developer stripped off from a developing roll 92 afterdevelopment to the developer agitation storage section B is disposedabove the developer agitation storage section B.

The magnet roll 96 is a roll member consisting of an alternating patternof S and N poles magnetized along the peripheral surface, as shown inFIG. 10A; magnetic poles having a strength of about 0.04 T aremagnetized at intervals of about 3 mm. The magnetic roll 96 is rotatedin the direction of arrow D2 shown in FIG. 9, thereby generating achanging magnetic field in the developer agitation storage section B.The peripheral speed of the magnetic roll 96 is determined appropriatelybetween 0.1 and 20 as a ratio between the peripheral speeds of themagnetic roll 96 and the development roll 92; it is set to about threetimes the peripheral speed of the development roll 92.

The guide member 94 is placed near between a developer supplying memberand a stripping-off member of the developing roll 92 and is coated onthe peripheral surface with a carrier coat agent, etc., along which adeveloper stripped off from the developing roll 92 slips down. PositionA at which the developer slips down provides a toner excess supplyingmember where an excessive amount of toner is supplied across thepartition 98 from the toner storage section 100. This supply method isto supply toner as much as consumed by providing a constant wide spacefor toner.

The developing roll 92 contains a magnetic field generation member 101comprising a plurality of magnetic poles like the developing roll 2shown in FIG. 1. The magnetic poles have a strength of 0.08 T, 0.06 T,0.07 T, 0.07 T, and 0.06 T in the rotation direction of a sleeve 102from magnetic pole 101a respectively.

The developing apparatus is the same as that shown in FIG. 1 in othercomponents.

In the development apparatus, a developer stripped off from thedeveloping roll 92 after development slips down along the guide member94 and an excess of toner is supplied by rotation of a paddle 95, thenis guided by gravitation into the developer agitation storage section Bwhere a changing magnetic field is formed by rotation of the magneticroll 96. The developer is transported along the curved face of the wallface 100b by the action of the magnetic field and circulates asindicated by the arrow shown in FIG. 9. As the developer circulates, itis agitated and toner comes in contact with carrier and is charged. Atthis time, the developer is agitated by the action of the magnetic fieldin a state in which the toner density is raised. Thus, developer stresslessens in comparison with agitation of the developer by mechanicalmeans. That is, when the developer is agitated by the action of themagnetic field, an ear of carrier is set and the carrier itself forms anagitation member at one moment and at the next moment, the ear of thecarrier is released and the surface area of the carrier in creases. Thecarrier and toner are scrubbed with each other reasonably by repeatingthe state, and easy charging is enabled under low stress in comparisonwith the case where a mechanical force is exerted on the carrier andtoner so that they are scrubbed with each other for contact charging.

The developer thus agitated circulates in the arrow direction and ispulled up. Also, it is attracted by the magnetic pole 101b of thedeveloping roll 92. At this time, excessive toner having a smalladhesion force to the carrier is screened out by collision resultingfrom agitation of the developer and by the gravity imposed on thedeveloper, whereby the excessive toner in the developer is separated andthe developer having the toner density matching the carrier chargecapability is supplied to the developing roll 92. Thus, the chargeamount of toner transported to the developing area becomes almostconstant, providing an image stable in density.

The developing apparatus uses the magnet roll 96 consisting of analternating pattern of S and N poles magnetized along the peripheralsurface, as shown in FIG. 10A. Instead, it may use a magnet roll with Sand N poles alternately magnetized in a spiral fashion along thecircumferential direction, as shown in FIG. 10B. Further, the developingapparatus may use a magnet roll with S and N poles alternatelymagnetized in a spiral fashion substantially symmetrical from theneighborhood of the center, as shown in FIG. 10C. As such a magnet rollrotates, a changing magnetic field can be formed in the developeragitation storage section B and the developer can be well agitated andcirculated.

FIG. 11 is a schematic diagram to show the configuration of a developingapparatus of another embodiment of the invention.

The developing apparatus comprises a mesh member 119 disposed below apartition 118 in housing 120 between a toner storage section 120a and adeveloper agitation storage section B in addition to the members of thedeveloping apparatus shown in FIG. 9.

The mesh member 119 has a large number of openings of the size forblocking a carrier and allowing toner to pass therethrough; in theembodiment, each opening is set to the size of about 30 μm because thecarrier diameter is 50 μm and the toner diameter is 7 μm. Any desiredmaterial can be selected for the mesh member 119; preferably the meshmember 119 is coated with fluororesin, a carrier coat agent, etc., likea guide member 114.

The developing apparatus is the same as that shown in FIG. 9 in othercomponents.

In the developing apparatus, excessive toner separated when a developeris agitated and circulated in the developer agitation storage section Bpasses through the openings of the mesh member 119 and is recovered to atoner storage section 120a. Thus, toner separated by the operation of amagnet roll 116 can be transported to a toner excess supplying member;toner can be again supplied smoothly. The developing apparatus cansupply a developer stable in toner density to a developing roll 112 evenwhen a comparatively small amount of magnetic carrier (about 100 g orless) is contained.

To prevent the mesh member 119 from being clogged, the mesh member 119may be shaken as it comes in contact with a film member attached to thetip of a paddle.

FIG. 12 is a schematic diagram to show the configuration of a developingapparatus of one embodiment of the invention.

The developing apparatus comprises a plurality of electromagnets 136arranged along a wall face 140b of a housing 140 and a power supply unit139 for controlling a current direction and timing for energizing theelectromagnets 136 in place of the magnet roll 96 of the developingapparatus shown in FIG. 9. Wall face 140b is separated from a tonerstorage section 140a by a partition 138.

The electromagnets 136 are connected to the power supply unit 139 inparallel and are controlled so as to generate alternating fields withphase differences when they are energized. The developing apparatus isthe same as that shown in FIG. 9 in other components.

In the developing apparatus, a developer in the developer agitationstorage section B is transported along the wall face 140b as in thedeveloping apparatus shown in FIG. 9 by alternating fields generated bythe electromagnets 136 and is circulated in the arrow direction shown inFIG. 12, whereby toner is charged and toner having a small adhesionforce to carrier is separated and the developer having the toner densitymatching the carrier charge capability is supplied to a developing roll132.

In the developing apparatus according to the invention of aspect 10,magnetic field generation means can be set appropriately if it generatesmagnetic field for transporting and circulating the developer in thedeveloper agitation storage section B. In addition to the magnet rollused with the developing apparatus shown in FIG. 10 or 11 or theelectromagnets used with the developing apparatus shown in FIG. 12, anendless belt with an alternating pattern of S and N poles magnetized maybe circumferentially rotated by driving a support roll.

FIG. 13 is a schematic diagram to show the configuration of a developingapparatus of one embodiment of the invention.

The developing apparatus is opposite to the developing apparatus shownin FIG. 1 in rotation direction of developing roll 152 and comprises adeveloper recovery mix chamber 160b to which a developer passing througha developing area is recovered, at a position facing the lower part ofthe developing roll 152. A toner storage chamber 160c where tonerpassing through a mesh member 156 drops is disposed above the developerrecovery mix chamber 160b, and a slit opening 158 is made in a partitionbetween the toner storage chamber 160c and the developer recovery mixchamber 160b. The developer recovery mix chamber 160b and the tonerstorage chamber 160c are provided with augers 154 and 157 respectivelyfor agitating and transporting the contents. A developer supply chamber160a for supplying a developer to the top of the mesh member 156 isdisposed in the upper part of a housing 160, as is regulation member153, and contains a spiral auger 155 for supplying a developer throughan slit 159. Further, a developer passage 161 for transporting adeveloper to the developer supply chamber 160a is coupled to the axialend of the developer recovery mix chamber 160b.

The spiral auger 155 comprises a coupling plate 165 for coupling spiralelements as shown in FIG. 14 and the width of the coupling plate 165, d,is set so as to widen gradually in the developer transport direction.

The developing apparatus is the same as that shown in FIG. 1 in othercomponents.

In the developing apparatus, the developer after development is strippedoff by the action of repulsion magnetic poles of the developing roll 152and is transported axially by the auger 154 in the developer recoverymix chamber 160b. An excess of new toner is supplied from the tonerstorage chamber 160c and is agitated together with a recovereddeveloper. The resultant developer is transported on a developertransport passage 161 to the developer supply chamber 160a. In the tonerstorage chamber 160c, toner recovered through the mesh member 156 isreplenished with new toner from a toner box (not shown). The resultanttoner is supplied to the developer recovery mix chamber 160b as newtoner.

On the other hand, the developer transported to the developer supplychamber 160a is transported axially by the spiral auger 155. At thistime, by translational motion by rotation of the spiral auger 155 andthe action of the coupling plate 165, the developer is combed up in adirection perpendicular to the translational motion direction and isswept out through the slit 159. At the time, the coupling plate 165 hasa width gradually widening in the developer transport direction and thesweep-out amount and the transport amount of the translational motionare well balanced, so that an almost equal amount of developer issupplied through the slit 159 to the top of the mesh member 156.

The developer fed onto the mesh member 156 is a developer mixed with anexcess of toner, and slips down along the slope of the mesh member 156by gravitation. At this time, redundant toner having a small adhesionforce to carrier drops through the mesh member into the toner storagechamber 160c, whereby the developer on the mesh member 156 is adjustedto the toner density matching the carrier charge capability.

On the other hand, the redundant toner screened out into the tonerstorage chamber 160c is agitated together with fresh toner transportedfrom the toner box (not shown) by the auger 157 and the resultant toneris supplied excessively to a recovered developer as supply toner throughthe opening 158. The supply timing of the fresh toner is set by usingknown means, such as pixel count or solid batch sense.

Although the width of the coupling plate 165 of the spiral auger 155 isset to axially different dimensions in the developing apparatus, thewidth of the coupling plate 165 may be made uniform and the slit forsupplying a developer may be formed so as to widen gradually toward thedeveloper transport direction. That is, the amount of the developerbeing transported by the spiral auger decreases as the developer goesdownstream in the transport direction, but the slit is widened in thedeveloper transport direction, whereby toner is easily dischargedgradually and an almost equal amount of developer in the transportdirection flows out.

As we have discussed, the developing apparatus according to theinvention supplies an excess of toner to a developer, then screens outtoner having a small adhesion force to magnetic carrier for supply tothe developer transport member, so that the toner density and chargeamount of the developer transported to the developing area can bemaintained almost uniform and a stable image density can be providedover a long term. Complicated toner density control means as usedformerly is not required, decreasing costs and downsizing the apparatus.The invention can also be applied to a developing apparatus storing acomparatively small amount of developer. If the invention is applied tocolor image formation, stable and good developing can also be executed.

What is claimed is:
 1. A developing apparatus using a dual-componentdeveloper containing a magnetic carrier and toner electrically attractedto the magnetic carrier for selectively transferring the toner to anelectrostatic latent image formed on an image support for visualizingthe latent image, said developing apparatus comprising:a developertransport member adapted to face the image support, having a rotatableperipheral surface for supporting and transporting the developer; atoner excess supplying member for containing developer to be supplied tothe developer transport member and for supplying an excess of toner tothe developer; excessive toner separation means for separating tonerhaving a small adhesion force to the carrier from the developer to whichexcessive toner is supplied; and a recirculator for transporting thetoner separated from the excessive toner separation means to the tonerexcess supplying member.
 2. The developing apparatus of claim 1, whereinsaid developer transport member comprises;a magnetic field generationmember having a plurality of magnetic poles along the peripheral surfacethereof, and a sleeve making circumferential rotation outside saidmagnetic field generation member, and wherein said toner excesssupplying member is disposed in an area which is not affected by amagnetic carrier attraction force of said magnetic field generationmember.
 3. The developing apparatus of claim 1, whereinsaid developertransport member comprises;a magnetic field generation member having aplurality of magnetic poles along the peripheral surface thereof, and asleeve making circumferential rotation outside said magnetic fieldgeneration member, wherein said toner excess supplying member isdisposed at a position along an outer peripheral surface of said sleeve,and wherein a plurality of magnetic poles are disposed in acircumferential direction in a portion of said magnetic field generationmember facing said toner excess supplying member as an alternatingpattern of N and S poles.
 4. The developing apparatus of claim 1,whereinsaid excessive toner separation means comprises;a sieve memberprovided with a large number of openings each of which has a size forblocking the magnetic carrier and allowing toner to pass therethrough soas to screen out excessive toner from the developer.
 5. The developingapparatus of claim 4, further comprising:shaking means for shaking saidsieve member.
 6. The developing apparatus of claim 5, whereinsaidshaking means is disposed so as to come in contact with said sievemember for mechanically shaking said sieve member.
 7. The developingapparatus of claim 5, whereinsaid shaking means is an electrode memberdisposed facing said sieve member, an AC voltage being applied to saidelectrode member.
 8. The developing apparatus of claim 4, furthercomprising:a member for shaking the developer on said sieve member. 9.The developing apparatus of claim 1, whereinsaid excessive tonerseparation means comprises:magnetic field generation means with analternating pattern of N and S poles magnetized along an outerperipheral surface; and a sleeve having a peripheral surface supportedfor circumferential rotation outside said magnetic field generationmeans for magnetically attracting the developer on the peripheralsurface thereof and transporting the developer.
 10. The developingapparatus of claim 1, whereinsaid excessive toner separation meanscomprises;magnetic field generation means for generating a changingmagnetic field for agitating, pulling up the developer in saiddeveloping apparatus by a magnetic force, and supplying the developer tothe peripheral surface of said developer transport member.
 11. Thedeveloping apparatus of claim 10, whereinsaid magnetic field generationmeans is a magnet having a plurality of magnetic poles, and beingrotatably supported behind a wall face of a housing for storing thedeveloper.
 12. The developing apparatus of claim 11, whereinsaidmagnetic field generation means is a roll member with an alternatingpattern of S and N poles magnetized on a peripheral surface thereof. 13.The developing apparatus of claim 10, whereinsaid magnetic fieldgeneration means is a plurality of electromagnets arranged along a wallface of a housing for storing the developer, said developing apparatusfurther comprising;a power supply unit for controlling a currentdirection and timing for energizing said plurality of electromagnets.14. The developing apparatus of claim 1, wherein the toner excesssupplying member comprises a guide plate for directing developer carriedby the developer transport member toward the excessive toner separationmeans.
 15. The developing apparatus of claim 1, wherein the recirculatorcomprises a housing adapted to contain toner separated by the excessivetoner separation means, and a member movable within the housing totransport separated toner from the housing to the toner excess supplyingmember.
 16. The developing apparatus of claim 15, wherein the movablemember is a rotatable arm disposed within the housing.
 17. Thedeveloping apparatus of claim 15, wherein the movable member is adaptedto contact and shake the excessive toner separation means.